I. Field of the Invention
The present invention relates to both a system and method for identifying a type of gas.
II. Description of the Prior Art
Many modern day vehicles utilize a combustible gaseous fuel in lieu of, or in addition to, a liquid fuel system. Such liquid fuel systems typically include both gasoline as well as diesel fuels.
There are currently several different types of gaseous fuels utilized with motor vehicles. For example, such currently utilized gaseous fuels include both propane and methane or mixtures thereof.
In order to provide for the efficient combustion of the fuel within the gaseous fuel engine, it is necessary to monitor the mass flow rate or velocity of the gaseous fuel to the engine. In order to obtain this information, mass flow sensors, also known as hot wire or hot element flow sensors, are fluidly connected in series between the source of the gaseous fuel and the engine so that the gaseous fuel flows through the flow meter. The flow meter then produces an electrical output signal proportional to the mass flow rate of the gaseous fuel and this output signal is coupled as an input signal to a microprocessor based electronic control unit (ECU) which controls the engine combustion for the vehicle. Such control of the engine combustion is necessary to not only maximize fuel efficiency, but also to minimize any noxious emissions.
These previously known hot wire mass flow sensors, however, inherently produce a nonlinear output signal in response to the gaseous flow through the sensor. Consequently, the previously known gas flow sensors are conventionally designed for a predetermined type of gas, for example a gas flow sensor for propane or a gas flow sensor for methane, and each flow sensor utilizes its own unique calibration curves to determine the actual mass flow rate from the output of the mass flow sensor. Furthermore, conventional hot wire sensors utilize a bridge circuit and an internal resistor to compensate for temperature variations. This internal temperature resistance compensation, however, varies from one gas to another type of gas. Consequently, a mass flow rate through these previously known hot wire mass flow sensors will vary depending upon the type of gas even for the same mass flow rate through the sensor.
In order to achieve efficient, pollution free and, indeed, safe operation of an internal combustion engine, the type of gaseous fuel utilized in the engine must be known by the ECU before the ECU can control the proper engine combustion for the engine. Consequently, most gaseous fuel internal combustion engines are designed and calibrated for a single type of gaseous fuel. However, there are situations where the wrong type of gaseous fuel may be supplied to the gaseous fuel engine or other situations in which operation of the engine by using two or even more different types of gaseous fuels is desirable such as liquid propane gas and compressed natural gas.
The identification of the gas type is also desirable in other types of gaseous systems, such as fuel cell applications.
Today, there are no known systems or methods for determining the type of gaseous fuel provided to an internal combustion engine.
The present invention provides both a method and system for identifying the type of gas provided to an internal combustion engine or other gaseous systems.
In brief, the system of the present invention comprises a first sensor in contact with the gas. This first sensor provides a first electrical output signal indicative of a first condition of the gas.
Similarly, a second sensor is also in contact with the gas. This second sensor also provides a second output signal indicative of a second condition of the gas. The first and second conditions may be the same gas characteristic, e.g. the mass flow rate of the gas, but utilizing flow sensors with different calibrations.
The output signals from both of the sensors are coupled as input signals to a microprocessor based processing means. The processing means then compares the outputs from the sensor, often at two or more different operating conditions, to presorted lookup tables from which the gas type can be determined. Alternatively, the processing means can determine the gas type by calculation based upon the output signals from the sensors.
Furthermore, the first and second conditions of the gas are selected from the group of temperature, mass flow rate (which is directly proportional to gas velocity), temperature and pressure.